Page:Popular Science Monthly Volume 89.djvu/324

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��Popular Science Monthly

��Surveying Instrument

���The tripod and sighting in- strument are constructed of simple materials

TO make a practical surveying instru- ment, take a piece of tin or sheet- iron two ins. wide and sixteen ins. long; a piece of 7-8 in. wood shaped like a triangle, three ins. on a side; three strips of wood as long as the distance from the ground to a little above your eyes when you are standing erect; one lath one foot long; and a wing-bolt.

Bend up the strip of metal two ins. from each end so as to form right angles. Rcginiiing ]/i in. from the top of the bent portions and extending to }4 in. of the bottom, cut a slit >^ in. wide to sight through. Screw or nail the metal strip to the short lath. Drill a hole in the middle of this apparatus to correspond with the size of the wing-bolt, and one in the center of the triangle.

Now make a tripod by hinging one of the three long strips to each side of the triangle. Pnt a nail, with the head tiled off, in the bottom of each leg to lorm three anchoring points.

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��To Re- Silver Old Mirrors

iRST take off all the old silver by the use of nitric acid. Rinse with clear water and wipe off edges with a cloth. Polish the surface of the side of the glass to be silvered with rouge, so as to remove grease and any foreign matter. Then clean the rouged surface off with a brush and a solution of chloride of tin and water.

After cleaning thoroughly rin.se with clear water and lay glass on a flat table that is level, being careful not to touch the surface.

Next make a solution of ^2 oz. silver nitrate precipitate in ammonia with 8 ozs. of distilled water. Dilute yi oz. of Rochelle salts in 8 ozs. of distilled water.

After these solutions are made and the glass cleaned and ready for the silver, take about 8 drahms of silver solution and 6 drahms of salts, mix, and pour same on glass with enough distilled water to flood the glass. Within three hours the glass will be resilvered.

Temporary Pole- Steps of Spikes

THE wireless amateur interested in outside aerials for his wireless equipment will soon find a demand for safe and substantial pole-steps on which he can climb Nature's antenna poles — the trees. Usually he drives in a nail at some close angle. But this is very un- safe, as he may loose his footing when he least expects it. In the method illustrated two 5-in. spikes are used in making each pole- step, one spike being driven at a horizontal line, and the other directly beneath it at an angle of 45 degrees. The one at 45 de- grees is dri\en in first, and then the straight one. The horizontal step has a tendency to de- press the one on which it rests, and results in the form- er being d r i \' e n Heavy splices make deeper into the serviceable steps pole or tree trunk.

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